Various forms of exercise boards or machines are disclosed in the following U.S. patents: Harrison, U.S. Pat. No. 1,950,174, dated May 27, 1932; Walker, U.S. Pat. No. 3,709,487, dated Jan. 9, 1973; Pridgen U.S. Pat. No. 3,834,694, dated Sept. 10, 1974; and Kirk U.S. Pat. No. 3,966,200, dated June 29, 1976.
In Harrison Pat. No. 1,950,174 the frame is supported on legs with braces and at each end of the frame is an adjustable extension providing a cross bar for connection of springs equipped with hand grips and ankle fasteners, the body of the person using the Harrison machine being supported on a carriage which is longitudinally slidable on the frame so that when the arms are exercised the springs connected to the ankles stretches the legs of the person as the carriage moves from the cross bar to which the ankle connecting springs are secured.
The Walker Pat. No. 3,709,487 discloses a complex form of foldable exercise apparatus which provides an inclined body supporting board for performing various exercises in connection with hand grips having springs hooked thereto and to the bottom of a support stand, and in one inclined position, the board constitutes a slant board in which the legs are secured to the upper end of the board for performing sit-ups and like exercises. The Walker exercise apparatus (when the board is removed or repositioned) enables performance of various exercises including chinning and lift-off exercises.
The Pridgen Pat. No. 2,834,694 discloses a leg exercising apparatus which includes a complex arrangement of pulleys and weights and which has an accessory for exercising the groin muscles.
The Kirk Pat. No. 3,966,200 relates to a stretching exercise device whilch includes a generally rectangular body support board on which a hand grip bar and a foot retaining bar are longitudinally adjustable for body stretching exercises.